soname and real name

[1] https://wiki.openssl.org/index.php/OpenSSL_1.1.0_Changes#Backward_compatibility

[2] https://akkadia.org/drepper/dsohowto.pdf, how to write shared libraries, 2011

[3] https://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html, 背下来，搜soname, real name, major, minor, release, compat, pic

The GNU linker uses the -hname or -soname=name to specify the library name field. Internally, the linker will create a DT_SONAME field and populate it with name.

-- soname - Wikipedia

gcc -fPIC -g -c -Wall a.c

gcc -fPIC -g -c -Wall b.c

gcc -shared -Wl,-soname,libmystuff.so.1

-o libmystuff.so.1.0.1 a.o b.o -lc

-- Shared Libraries[3]

soname提供了backward-compatible信息；如果soname不变，说明可以兼容。

下面RHEL7上的示例可以看出：

• so软链接规范，命名规范
  • 第二层文件名与soname一致
• openssl-1.0.2与openssl-1.1不兼容[1]。openssl的版本号与一般linux动态库不太一样,openssl3已回归潮流。
• ld链接的实际上是第二层文件名（共3层），带了版本号；可以认为是major版本号，保证兼容性。

$ ls -l /usr/lib64/libssl.so*
lrwxrwxrwx  1 root root     16 Jun  7 13:48 /usr/lib64/libssl.so -> libssl.so.1.0.2k
lrwxrwxrwx. 1 root root     16 Sep 19  2018 /usr/lib64/libssl.so.10 -> libssl.so.1.0.2k
-rwxr-xr-x. 1 root root 470360 Apr 11  2018 /usr/lib64/libssl.so.1.0.2k

$ objdump -p /usr/lib64/libssl.so.1.0.2k | grep -i name
  SONAME               libssl.so.10

$ objdump -p /lib/x86_64-linux-gnu/libssl.so.1.1 | grep -i name
  SONAME               libssl.so.1.1

$ ls -l /usr/lib64/libpcre.so*
lrwxrwxrwx. 1 root root     16 Jul 10 22:59 /usr/lib64/libpcre.so -> libpcre.so.1.2.0
lrwxrwxrwx. 1 root root     16 Jul 10 16:47 /usr/lib64/libpcre.so.1 -> libpcre.so.1.2.0
-rwxr-xr-x. 1 root root 402384 Aug  2  2017 /usr/lib64/libpcre.so.1.2.0

$ objdump -p /usr/lib64/libpcre.so.1.2.0 | grep -i name
  SONAME               libpcre.so.1

$ ldd /usr/bin/ssh
	linux-vdso.so.1 =>  (0x00007ffc693e6000)
	libfipscheck.so.1 => /lib64/libfipscheck.so.1 (0x00007fc341f60000)
	libselinux.so.1 => /lib64/libselinux.so.1 (0x00007fc341d39000)
	libcrypto.so.10 => /lib64/libcrypto.so.10 (0x00007fc3418d6000)
	libdl.so.2 => /lib64/libdl.so.2 (0x00007fc3416d2000)
	libldap-2.4.so.2 => /lib64/libldap-2.4.so.2 (0x00007fc34147d000)
	liblber-2.4.so.2 => /lib64/liblber-2.4.so.2 (0x00007fc34126e000)
	libutil.so.1 => /lib64/libutil.so.1 (0x00007fc34106b000)
	libz.so.1 => /lib64/libz.so.1 (0x00007fc340e55000)
	libcrypt.so.1 => /lib64/libcrypt.so.1 (0x00007fc340c1e000)
	libresolv.so.2 => /lib64/libresolv.so.2 (0x00007fc340a04000)
	libgssapi_krb5.so.2 => /lib64/libgssapi_krb5.so.2 (0x00007fc3407b7000)
	libkrb5.so.3 => /lib64/libkrb5.so.3 (0x00007fc3404ce000)
	libk5crypto.so.3 => /lib64/libk5crypto.so.3 (0x00007fc34029b000)
	libcom_err.so.2 => /lib64/libcom_err.so.2 (0x00007fc340097000)
	libc.so.6 => /lib64/libc.so.6 (0x00007fc33fcc9000)
	libpcre.so.1 => /lib64/libpcre.so.1 (0x00007fc33fa67000)
	/lib64/ld-linux-x86-64.so.2 (0x00007fc342421000)
	libsasl2.so.3 => /lib64/libsasl2.so.3 (0x00007fc33f84a000)
	libssl.so.10 => /lib64/libssl.so.10 (0x00007fc33f5d8000)
	libssl3.so => /lib64/libssl3.so (0x00007fc33f37b000)
	libsmime3.so => /lib64/libsmime3.so (0x00007fc33f153000)
	libnss3.so => /lib64/libnss3.so (0x00007fc33ee1e000)
	libnssutil3.so => /lib64/libnssutil3.so (0x00007fc33ebee000)
	libplds4.so => /lib64/libplds4.so (0x00007fc33e9ea000)
	libplc4.so => /lib64/libplc4.so (0x00007fc33e7e5000)
	libnspr4.so => /lib64/libnspr4.so (0x00007fc33e5a7000)
	libpthread.so.0 => /lib64/libpthread.so.0 (0x00007fc33e38b000)
	libfreebl3.so => /lib64/libfreebl3.so (0x00007fc33e188000)
	libkrb5support.so.0 => /lib64/libkrb5support.so.0 (0x00007fc33df78000)
	libkeyutils.so.1 => /lib64/libkeyutils.so.1 (0x00007fc33dd74000)
	librt.so.1 => /lib64/librt.so.1 (0x00007fc33db6c000)

ABI-compatible检测工具

• https://lvc.github.io/abi-compliance-checker/
• https://wiki.openssl.org/index.php/Binary_Compatibility